Hispanic youth in the juvenile justice system are at increased risk of HIV infection and of using illicit drugs. The proposed study's overarching goal is to reduce the ethnic disparities in illicit drug use and HIV between Hispanic and non-Hispanic youth in the criminal justice system. The proposed 2-year study will be guided by four aims. AIM 1 is to evaluate the efficacy of Familias Unidas, relative to Treatment as Usual in preventing illicit drug use in a sample of Hispanic youth first offenders;AIM 2 is to evaluate the efficacy of Familias Unidas, relative to Treatment as Usual in preventing unsafe sexual behavior;AIM 3 is to evaluate the efficacy of Familias Unidas, relative to Treatment as Usual in reducing the number of subsequent criminal offenses;and AIM 4 is to assess the extent to which family functioning mediates the effects of the intervention on illicit drug use, unsafe sexual behavior, and subsequent criminal offenses. 240 Hispanic adolescent first offenders (age range 13 to 17) and their parents will be randomized to either Familias Unidas or Treatment as Usual. Youth and parent participants will be assed at baseline, post-intervention (i.e., 6-months post baseline), and 12-months post baseline. The Familias Unidas intervention has been evaluated and found to be efficacious in two randomized trials. In the first study (Pantin et al., 2003), Familias Unidas was shown to be efficacious relative to a no intervention control condition in increasing family functioning and reducing behavior problems. In the second randomized trial (Prado et al., 2007), Familias Unidas was found to be efficacious, relative to two attention control conditions, in reducing illicit drug use and unprotected sexual behavior at last sexual intercourse. In both trials, family functioning was found to mediate the effects of condition on the outcomes. Hierarchical Linear Modeling (HLM) will be used to test: (H1) Familias Unidas will be more efficacious than Treatment as Usual in reducing illicit drug use over time;(H2) Familias Unidas will be more efficacious than Treatment as Usual in reducing unprotected sexual behavior use over time;and (H3) Familias Unidas will be more efficacious than Treatment as Usual in preventing subsequent criminal offenses. Additionally HLM will be used to determine whether (H1a) the effect of Familias Unidas on illicit drug use will be partially mediated by family functioning;(H2a) the effect of Familias Unidas on unprotected sexual behavior will be partially mediated by family functioning and (H3a) the effect of Familias Unidas on subsequent criminal offenses will be partially mediated by family functioning.